drop down menus won't stop 2650

Our Inspiron 2650 has a problem.  For no reason, drop down menus appear, like I am right clicking on various items on the screen, but I am not.  In fact, sometimes I'll just be sitting there, not typing, and one will pop up.  I'll left click or tap the pad and it goes away. 

Then one of 2 things happens:  1)  As soon as it disappears, it reappears and I sit there tapping the pad for a dozen times until the menu stays away.

                          2)  It will remain gone after one tap anywhere for a few seconds up to several minutes.  

 

This same thing happened a few months back and then our computer crashed.  We bought a new hard drive and everything has been working for a few months and now the menu thing is happening again. 

    We've never spilled anything on the keyboard, but could it be electrical? 

Any ideas?

Is this something that is covered under our extended warrenty?

Thanks

Paul B.